EMI Suppression Filters (EMC and Noise Suppression)Noise Suppression Measures for HDMI 2.1

Contents

HDMI 2.1 has a maximum bandwidth that is about 2.7x that of HDMI 2.0, and its maximum signal transmission speed per lane is twice that of HDMI 2.0.
Whereas HDMI 2.0 consists of three data lanes and a clock lane, HDMI 2.1 does not have a clock lane, and it consists of four data lanes.

In this way, HDMI 2.1 transmits signals faster than before, and so care must be taken to ensure that the signal quality is not harmed when implementing noise suppression measures.

Two noise issues are conceivable when HDMI communication is performed.

This study focuses on the intrasystem EMC of radiation noise ① and examines corrective actions for it.

If normal noise filters are used for high-speed differential signaling lines like HDMI, the signal quality will deteriorate, and the signals will not be transmitted properly. For this reason, common mode choke coils (CMCC) are a suitable solution. Because HDMI signals are high speed, we should select a CMCC that is best suited for high-speed signals.
CMCCs are installed near the output pins of the IC at the HDMI source side and near the connectors at the sink side. The source-side CMCC installed near the IC can suppress the common mode noise generated from the transmission ICs at the source side by preventing the propagation of common mode noise at the sink side.
The sink-side CMCC can suppress the common mode noise generated from the HDMI signal wiring of the sink equipment by preventing common mode noise from entering the Wi-Fi antenna.

An issue arose where the Wi-Fi reception sensitivity dropped during HDMI 2.1 communication, but this was improved by using CMCCs.

In HDMI 2.1, radiation noise occurred in the range from 1 GHz to 6 GHz, but this was improved by using CMCCs.

Inserting CMCCs had no effect on the eyemask test.
Use of CMCCs reduced the AC common mode voltage.